As an injector for injecting a fertilized ovum or a sperm for artificial insemination into the uterus of an animal such as a cow, an injector which comprises an injection pipe composed of a flexible tube inserted in a guide pipe and a nozzle connected at the frontal end of the injection pipe has been proposed (see, Patent Document 1). When injecting a fertilized ovum or a sperm using such an injector, a guide pipe in a state where an injection pipe is pulled inside the guide pipe is inserted through the vaginal opening into the uterine body, and then a frontal end of the injection pipe is pushed out from a frontal tip of the guide pipe by manipulating a protruding portion of a flexible tube constituting the injection pipe that protrudes from the rear side of the guide pipe so that the nozzle can reach a deep part of the uterine horn. Next, a sperm etc. is supplied from the rear side of the injection pipe to the nozzle to discharge the sperm etc. from the nozzle, and then the injector is pulled out through the vaginal opening.